1. Field of the Invention
The present invention relates generally to lubrication of a rotary machine. More particularly, the present invention relates to lubrication of a rotary machine of the class wherein a pair of vertically spaced parallel shafts are rotated in a synchronized relationship through a train of gears and wherein the upper shaft has an oil seal and a bearing that require lubrication and that are located vertically remote from an oil sump of the machine. The present invention is specifically applicable to the lubrication of a Roots blower used as a supercharger in an automotive engine. However, the invention is not limited to such application.
2. Description of the Related Art
A Roots blower is known as having a pair of two-lobe cycloidal rotors rotated within a housing in opposite directions with an angular phase difference of 90.degree. to perform a pumping action. Each rotor is mounted on an associated shaft which is journaled to the housing through antifriction bearings. Generally, an external driving power is applied to one of the two shafts, i.e., the drive shaft. The other shaft, i.e., the driven shaft, is rotated in synchronization with the drive shaft through a pair of gears in mesh with each other and mounted on the free ends of the shafts extending outwardly from the housing.
To provide lubrication and protection of the gears, a gear cover is secured to the side plate of the housing to define therebetween a gear chamber surrounding the gears. This gear chamber also serves to define an oil sump for storing a lubricant which lubricates the bearings and the gears. Oil seals are provided between respective rotor shafts and the side plate of the housing to prevent the lubricant from seeping into the working chamber of the blower. These oil seals are located downstream of the bearings with respect to the direction of oil seepage. Practically, the lubricant is charged only in an amount of about one-fourth of the volume of the gear chamber in order to avoid an inevitable loss of drive power of the blower when the gear chamber is fully charged with the lubricant.
When a Roots blower is used as a supercharger for an automotive engine, it is customary to mount the blower in a vertical position so that one of the two rotor shafts is placed vertically above the other. In this situation, only a part of the lower gear, i.e., the gear mounted to the lower rotor shaft, is dipped in the oil sump. The lubricant in the sump is scooped up by the teeth of the rotating lower gear and is transferred onto the upper gear teeth to adequately lubricate the meshing gear surfaces. The lubricant will sufficiently lubricate the bearing and the oil seal associated with the lower rotor shaft since they are partly dipped in or located relatively close to the oil sump, although the amount of lubricant in the oil sump is reduced in order to obviate the afore-mentioned loss of drive power. The bearing and the oil seal associated with the upper rotor shaft, however, tend to be only poorly lubricated because the amount of lubricant transferred from the lower gear onto the upper gear is not only limited but the lubricant tends to spill sideways of the upper gear before being brought to the high level required to lubricate the bearing and oil seal of the upper shaft. This can result in a premature failure of the bearing and, in particular, of the oil seal of the upper rotor shaft. Various lubricating arrangements have been proposed to overcome this problem. For example, Japanese Unexamined Patent Publication No. 61-49185 discloses a specific rear cover design to improve lubrication of the upper shaft bearing and oil seal; Japanese Utility Model Application No. 60-000043 filed Jan. 7, 1985 proposes to provide an oil pool in the gear chamber; and Japanese Utility Model Application No. 60-021247 filed Feb. 19, 1985 proposes a lubricating arrangement having a guide plate adapted to direct the lubricant into inclined oil passages leading to the bearing and oil seal of the upper shaft. Although these arrangements have considerably improved lubrication, it is still desirable to positively prevent the lubricant from escaping sideways from the rotating lower and upper gears.